A conical-radial wave power divider/combiner has been studied, which has broadband and low loss characteristics required for the power dividing-combining system in order to realize microwave high power solid-state amplifiers. In this paper, the optimum design with the electromagnetic simulator for the divider is presented. The divider is composed of the central part in which the input coaxial line is transformed into the conical line followed by the radial line, and the peripheral part in which the coaxial probes are inserted into the radial line. Each part is designed in order to have wide bandwidth. The divider is constructed by connecting the optimum central and peripheral parts. The designed twelve-way divider has the relative bandwidth of 44% in which the return loss is less than -20dB. In the experiment, the wider relative bandwidth was achieved with 47%.